; . - 



DEPARTMENT OF COMMERCE 



Technologic Papers 



OK THE 



Bureau of Standards 

S. W. STRATTON, Director 



No. 192 
TESTS OF CENTRIFUGALLY CAST STEEL 



BY 



GEORGE K. BURGESS, Physicist 

Bureau of Standards 



JUNE 7, 1921 




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Sold oaly by the Superintendent o£ Documents, Government Printing Offic* 
Washington, D. C 

Washington 
government printing office 

1921 



DEPARTMENT OF COMMERCE 



Technologic Papers 



OF THE 



Bureau of Standards 

S- W. STRATTON, Director 



No. 192 
TESTS OF CENTRIFUGALLY CAST STEEL 



BY 



GEORGE K. BURGESS, Physicist 

ti 

Bureau of Standards 



JUNE 7, 1921 




PRICE, 10 CENTS 

Sold only by the Superintendent of Documents, Government Printing Office 
Washington, D. C. 



WASHINGTON 
GOVERNMENT PRINTING OFFICE 

1921 



^ 



^ 



LIBRARY OF CONGRESS 

RECEIVED 

0CT291921 

DOCUMENTS DIVISION 






TESTS OF CENTRIFUGALLY CAST STEEL 

By George K. Burgess 



ABSTRACT 

Six castings manufactured by the Millspaugh centrifugal process were examined as 
to their physical and chemical properties, including hardness, tensile strength, impact 
resistance, density, internal stress, segregation, soundness, and microstructure , both 
in the condition as cast and after various heat treatments. This investigation shows 
the possibilities of substituting heat treatment for forging in this type of casting. 



CONTENTS 

Page 

I. Introduction 3 

II. Dimensions of castings and of test samples 4 

III . Tests of castings 4 

1 . Hardness and chemical surveys 4 

2 . Density determination 7 

3. Investigation of stresses across section of rings 8 

4. Heat treatment and mechanical properties. . . 9 

5. Macrostructure and microstructure :'" '. 11 

IV. Summary 15 

I. INTRODUCTION 

In 191 8 the Bureau of Standards had occasion to examine sev- 
eral hollow steel cylinders made under the direction of W. H. 
Millspaugh by his centriiugal casting process. The manufacture 
of these centrifugal castings was carried out under somewhat ad- 
verse conditions in two steel foundries which, of course, due to the 
limited experimental nature of the trials, could not have developed 
the refined technique that practice would give, nor were efforts 
made to produce high-grade steel for these tests. 

The cylinders were cast in a machine revolving about its hori- 
zontal axis. The outer surface of the castings, of walls from 3% 
inches to % inch thick, were thus against the mold and turning 
faster than the free inner, cylindrical surface, which was last to 
ireeze. The outer surfaces were fairly smooth, but the interior 
surfaces were rough. 

The resttlts, comparing the several grades of steel in the con- 
dition as cast and after heat treatment, are of considerable inter- 
est as indicating what may be expected from this method in the 

3 



4 Technologic Papers of the Bureau of Standards 

production, for certain shapes, of sound steel, that is, free from 
physical defects and chemical segregation, and thus with prac- 
tically no waste material to discard. As will be shown, it is also 
a field particularly adapted to the elimination of forging and boring 
operations and the substitution for the former of heat treatment 
to produce the desired characteristics in the resulting product. 

II. DIMENSIONS OF CASTINGS AND OF TEST SAMPLES 

In all, six castings were examined, samples from which were 
subjected to the usual mechanical tests, both transverse and 
longitudinal, in the condition as cast and after various heat treat- 
ments. The characteristics of the metal with respect to internal 
stress, density, soundness, segregation, and microstructure were 
also studied 

In Figs, i and 2 are shown the dimensions of the castings and 
location of samples for test, except for No. 7, a cylindrical ring 12 
inches in diameter and having a wall thickness of % inch, from 
which longitudinal flat tensile bars 12 inches long by 1 inch by 
■& inch were taken. The tensile bars from all other castings 
were standard 2-inch round bars. Samples for chemical analysis 
were taken in ring turnings for Nos. 4, 5, and 7, and for Nos. 1,3, 
and 6 from longitudinal borings in zones numbered 1 to 5 from 
outside to inside of the casting (Figs. 1 and 2). 

III. TESTS OF CASTINGS 

1. HARDNESS AND CHEMICAL SURVEYS 

In Table 1 are given the results of the radial surveys for hard- 
ness and chemical analysis. It will be noted there is a gradual 
increase in carbon from the outside to the inside surface for all 
castings, this increase ranging from 0.02 per cent for No. 3 A to 
0.09 per cent for No. 5; it appears to be roughly proportional to 
the carbon content, or the percentage variation in carbon remains 
practically constant. The nickel and phosphorus appear to follow 
the carbon very closely in their behavior as to segregation; man- 
ganese and silicon, on the other hand, are nearly constant across 
the radial section; while sulphur, although somewhat erratic, in 
general is distributed similarly to carbon, as is also copper, although 
present in quantities less than 0.1 per cent. The hardness surveys, 
Brinell and scleroscope, follow closely the chemical segregation, 
the higher numbers occurring on the inside layers. A hardness 
survey with the scleroscope made midway along a longitudinal 
section the length (72 inches) of casting No. 1 at 3-inch intervals 



Tests of Centri fug ally' Cast Steel 5 

shows a gradual increase in hardness from end B to the middle, 
24.2 to 25.3, and then nearly uniform hardness foi the second half, 
or from center to end A. (See Fig. 1.) The chemical analysis of 




•^ 



a 
o 



S 



s 



s 



3 






<0 ^ kj 



the A and I sections, separated by 60 inches in casting No. 3, 
apparently shows evidence of longitudinal segregation, but this is 
so very slight as to be uncertain. 



Technologic Papers of the Bureau of Standards 




•ft, 



s 



o 



t3 



S 









Tests .of Centrifugally Cast Steel 

TABLE 1. — Results of Hardness and Chemical Surveys 



Num- 
ber 



Wall 
thick- 
ness 



Inches 
3* 



3A.. 



31... 



2i 



31 



3i 



Zone 



Hardness 



Brinell 



186 
186 
187 
187 
196 

160 
164 
167 
167 
160 

158 
159 
158 
156 
184 



125 
"l28' 
'l2i' 



249 



248 



245 

164 
166 
161 
167 
191 



123 



Sclero- 
scope 



25.8 
24.9 
25. 
25. 2 
25.7 

22.3 
22. 2 
22.4 
22.6 
22.3 

21.9 
22 
22.0 
22.5 
23.9 



19.7 
20.4 
20.6 
20.0 
19.2 



63.5 
60.6 
58.0 
55.5 
57.0 

23.4 
23.4 
23.4 
23.8 
25.2 



0.44 
.48 
.46 
.46 

.50 

.33 
.32 
.32 
.34 

.34 

.30 
.30 
.30 
.34 
.35 

.16 
.16 
.16 
.17 
.18 
.21 
.18 

.64 
.65 
.63 
.63 

.72 

.32 
.33 
.31 
.33 
.35 

.22 
.21 
.25 



Mn 



0.44 
.44 
.44 
.44 
.44 

.54 
.55 
.55 

.57 
.57 

.55 
.55 
.55 

.57 
.57 

.47 
.50 
.51 
.50 
.50 
.52 
.40 

.56 
.56 
.55 
.55 
.60 

.56 
.56 
.56 

.57 
.57 

.54 
.53 
.55 



Si 



.47 
.47 
.47 
.48 
.47 

.19 
.19 
.19 
.19 
.20 

.20 
.19 

.20 
.20 
.21 

.27 

.29 
.28 
.28 
.29 
.29 
.22 

.65 
.65 
.64 
.64 
.68 

.19 

.19 
.19 
.19 
.19 

.26 
.25 
.25 



0.024 
.030 
.032 
.032 
.034 

.022 
.030 
.032 
.034 
.030 

.031 
.030 
.030 
.030 
.030 

.054 

.045 
.045 
.049 
.053 
.060 
.066 

.033 
.032 
.029 
.031 
.033 

.034 
.035 
.039 
.032 
.033 

.026 
.026 
.026 



p 


Ni 


Cu 


0.011 


2.33 


0.084 


.013 


2.35 


.089 


.013 


2.32 


.085 


.014 


2.36 


.094 


.015 


2.39 


.089 


.015 


2.66 


.051 


.014 


2.67 


.053 


.015 


2.70 


.051 


.016 


2.75 


.055 


.017 


2.70 


.054 


.012 


2.66 


.062 


.013 


2.67 


.062 


.015 


2.68 


.067 


.017 


2.76 


.068 


.018 


2.60 


.065 


.045 






.033 






.033 






.037 






.038 






.043 






.059 






.014 


2.94 




.015 


2.92 




.015 


2.93 




.017 


2.93 




.017 


2.90 




.015 


2.69 


.059 


.015 


2.75 


.058 


.015 


2.72 


.059 


.015 


2.76 


.064 


.016 


2.81 


.064 


.013 






.014 






.016 













Cr 



0.04 



.04 



.04 



Tr 



.04 



2. DENSITY DETERMINATION 

A narrow circumferential strip 2 inches long, 1 inch broad, 
and % inch thick was cut from the outside and from the inside of 
a transverse ring from the nickel-steel casting No. 31 and from the 
low carbon casting No. 4 and used for determination of density. 
The results are as follows: 



Casting No. 



31 (outside) 
31 (inside). 

4 (outside) . 
4 (inside)". 



Density 

g/cm 3 
at 23°C 



7.838 
7.834 



7.834 
7.726 



Differ- 
ence 



+0. 004 



+0. 108 



<* The low density of sample No. 4 (inside) is probably due to the presence of a series of very fine pits or 
blowholes in this sample. These holes occur about one-sixteenth inch from the inner surface ot the casting, 
where their presence was actually observed. 



8 Technologic Papers of the Bureau of Standards 

3. INVESTIGATION OF STRESSES ACROSS SECTION OF RINGS 

Three concentric rings, three-eighths inch wide (radially) and 
one-halt inch thick (longitudinally), were cut from the No. 4 
casting (low-carbon electric-furnace steel, annealed), one ring 
from the outside, one midway, and one from the inside of the 
cylinder. Accurate measurements were made of the outside and 
inside diameters of each ring, the distance between diametrically 
opposite punch marks, and the distance between three sets of 
punch marks 2 inches apart, tangentially. A cut was then made 
(by a hand hack saw) midway between the 2 -inch tangential 
marks and at an angle of 90 to the diameter measured. When 
split thus the outer ring contracted visibly, but the middle and 
inner rings appeared to undergo no change. Similar rings were 
cut from casting No. 5 (high-carbon nickel steel, not annealed), 
measured and cut in the same manner as those from casting 
No. 4. 

TABLE 2. — Survey of Stresses in Concentric Rings from Castings 



Part 



Outside ring: 

Outside diameter 

Inside diameter 

Between punch marks (diam- 
eter) 

[outer 

Between tangential .... 

{middle.. 

punch marks . 

[inner 

Middle ring: 

Outside diameter 

Inside diameter 

Between punch marks (diam- 

etei) 

I outer 
middle. . 
inner 

Inside ring: 

Outside diameter 

Inside diameter 

Between punch marks (diam- 
eter) 

_ [outer 

Between tangential . Jjt . 

{middle.. 

punch marks . 

I.nner 



Casting No. 4 



Before 
split- 
ting 



Inches 

8.080 
7.280 
7.650 

2.030 
2.000 
1.920 

6.840 
6.560 
6.920 

1.985 
1.955 
1.900 

6.790 
5.980 
6.425 

1.970 
1.955 
1.945 



After 
split- 
ting 



Difference 



l 



Inches 

8.060 
7.265 
7.625 

1.990 
1.960 
1.890 

6.830 
6.550 
6.920 

1.985 
1.960 
1.900 

6.780 
5.975 
6.445 

1.965 
1.950 
1.945 



Inch 

0.020 contraction.. 

. 015 contraction. . 

. 025 contraction. . 

. 040 contraction. 
. 040 contraction. 
. 030 contraction. 

. 010 contraction. 

.000 

.000 

.000 

. 005 expansion. . 
.000 

. 010 contraction. 
. 005 contraction. 
. 020 expansion... 

. 005 contraction. 
. 005 contraction. 
.000 



Casting No. 5 



Before 
split- 
ting 



Inches 

10. 765 
10. 205 
10. 515 

2.015 
1.985 
1.990 

9.530 
9.080 
9.345 

2.000 
2.005 
2.000 

8.515 
8.360 
8.160 

1.985 
1.975 
1.975 



After 
split- 
ting 



Inches 

10. 750 
10. 185 
10. 505 

1.985 
1.950 
1.950 

9.565 
9.095 
9.355 

2.015 
2.020 
2.015 

8.560 
8.405 
8.175 

2.025 
2.005 
2.005 



Difference 



Inch 

0. 015 contraction 
. 020 contraction 
. 010 contraction 

. 030 contraction 
. 030 contraction 
. 040 contraction 

. 035 expansion 
. 015 expansion 
. 010 expansion 

. 015 expansion 
. 015 expansion 
. 015 expansion 

. 045 expansion 
. 045 expansion 
. 015 expansion 

. 040 expansion 
. 040 expansion 
. 040 expansion 



Tests of Centrifugally Cast Steel 9 

The measurements taken before and after cutting these eon- 
centric rings and the amount of expansion or contraction in each 
case are given in Table 2, and indicate the nature of the stresses in 
the outer, middle, and inner zones. A rough computation gives 
the compression at the outside ring of casting No. 4 as 48 000 
pound per square inch, and for No. 5 the compression at the 
outside ring is 31 000 pounds per square inch, and the tension at 
the inside ring is 47 000 pounds per square inch. These internal 
stresses are of the order of the elastic limits of the material, and, 
as would be expected, the outer zone of the casting is in com- 
pression. 

4. HEAT TREATMENT AND MECHANICAL PROPERTIES 

Turning now to the question of the improvement of these cast- 
ings by heat treatment, in Table 3 are given the details of the 
treatments to which material from the castings was submitted, 
and in Table 4 are grouped the mechanical properties associated 
with the respective treatments. The location of specimens is 
shown in Figs. 1 and 2. It should be recalled that castings Nos. 
1 , 3, 4, and 7 were annealed as a whole before any tests were made 
on them, while castings Nos. 5 and 6 were examined first in the 
condition as cast. The test pieces from 3A and 3/ were from 
pieces of the same casting 60 inches apart. An examination of 
Table 4 shows that most samples show good tensile strength for 
their composition and treatment and also that there is no marked 
difference in values for longitudinal and transverse specimens. The 
values for the Izod shock test are somewhat erratic. The ad- 
vantages of heat treatment, notably of the double quench and 
draw, in improving both the resistance to shock and especially 
the ductility as measured by reduction of area, are strikingly 
manifest. Certain of these treated steel castings would appear to 
compare very favorably in their properties with those of forged 
material of the same compositions. For example, the ordinance 
requirements for gun forgings are: Elastic limit, 65 000 pounds per 
square inch; tensile strength, 95000 pounds per square inch; 
elongation, longitudinal 22 per cent, transverse 18 per cent; con- 
traction of area, longitudinal 35 per cent, transverse 30 per cent. 
These are probably more than met by casting No. 6QQ (0 = 0.33, 
Ni = 2.75 per cent) and almost met by others such as 3AQ and 2,1 Q 
(C = 0.32, Ni = 2.70 per cent) . Again the properties of the casting 
41565°— 21 2 



IO 



Technologic Papers of the Bureau of Standards 



7 (C = 0.23 per cent) are high for steel castings of that composition, 
and in the treated condition are superior to many of the results 
on hot- rolled 0.20 to 0.25 per cent carbon steels and indeed are 
comparable to those ot cold-rolled steels of this grade. 



TABLE 3.— Heat Treatment 





Condi- 
tion 
received 


Heat treatment 
given 




Temperatures and time of heating 


Des- 
igna- 
tion 


Heated 
slowly 
in air 
at the 

follow- 
ing 

temper- 
atures 


Then 
cooled. 
Held 
the 
follow- 
ing 
num- 
ber of 
hours 


Temperature 
when quenched 


Quench- 
ing 
medium 


Drawn 

30 

minutes 

at — 




of 
sam- 
ple 


First 


Second 


Cooled 
in 


IN... 


Annealed 

...do 

. . .do 

...do 

...do 

do... 


Normalized 

Quenched and 
drawn. 

Quenched and 
drawn. 

Quenched and 

drawn. 
Double quenched . . 

Quenched and 
drawn. 


°C 

800-805 
800-805 

890-900 
890-910 

910-925 
910-925 

910-925 

750-760 
750-760 

850-860 
850-860 

850-860 
875-880 


2 
2 

3 
3 

2 

2 

2 
1* 

li 

2 

2 

2 
1 


°C 


°C 




°C 


Ah 


1Q... 


795-800 




Water. . . 


600 


Do. 


03N.. 




Do. 


3Q... 


845-850 




Oil 


640-650 


Do. 


4N... 




Do. 


4Q-. 


915-925 
915-925 




Water. . . 
...do 


450-460 
440-450 


Do. 


4QQ- 

5N. 


...do 

As cast 
do. 


885 


Do. 
Do. 


5Q. 


760 




Oil 


700-705 


Do. 


6N 


do.. . 




Do. 


6Q... 
6QQ. 

7Q... 
7QQ. 


..do 

...do 

Annealed 
...do 


Quenched and 

drawn. 
Double quenched . . 

Quenched and 

drawn. 
do 


825-830 
825-830 

875-880 
880-885 




Water. . . 
...do 

...do 


675-680 
680-690 

510-515 
435 


Do. 


790-795 


Do. 
Do. 


880-885 1 


845 


...do 


Do. 











° Specimens from A and I sections of No. 3, same treatment. 



Tests of Centrifugally Cast Steel 

TABLE 4. — Mechanical Properties 



II 



CandNi 


No. 


Yield point 
(Divided by 

1000) 


Ultimate 
strength 
(Divided 
by 1000) 


Elonga- 
gation 
in 2 in. 


Reduc- 
tion of 
area 


Izod im- 
pact 


Microstructure 




L 


T 


L 


T 


L 


T 


L 


T 


L 


T 






[IX 
IY 
IT 

IN 
IQ 

f3AX 
3AY 

hAT 
3AN 

13AQ 

(31X 
I31Y 
131N 
|31Q 

ft 
4N 
4Q 
4QQ 

]5N 
Uq 

[6X 

6Y 

6T 
16N 

6Q 
16QQ 

[7N 

17QQ 


Lb 


Lb 


Lb. 


Lb. 


10.5 
9.5 

8.5 
4.5 

7.5 
16.5 

16.0 
21.5 

14.8 

27.0 

9.5 

21.0 

16.5 
11.5 
13.0 
12.5 

2.5 

6.5 

16.5 

17.5 
17.5 

14.5 
16.5 
23.0 

35.5 
18.3 
27.3 


5.5 
6.5 

26.6 
20.5 

1.0 

"i.'s 

16.5 
12.5 


12.1 
8.9 

12.5 
11.5 

12.1 
22.0 

29.3 
47.4 

19.3 
41.8 
18.5 
29.9 

10.4 
18.9 
20.3 
24.5 

1.2 

5.4 

21.7 

21.5 
28.5 

22.0 
26.5 
44.0 

52.5 
39.2 
47.7 


7.5 
14.0 

42.~5 
42.0 

1.0 
10.5 

22.6 
24.5 


Ft. 
lb 


Ft. 
lb. 






in.2 

54.3 
53.5 

67.5 
87.5 

53.8 
48.5 

59.8 
67.5 

52.5 
48.4 
60.5 
64.5 

40.0 
47.5 
60.0 
55.0 

48.0 
77.5 
96.4 

47.5 
48.0 

60.0 
83.5 
70.0 

38.0 
69.3 
57.8 


in.2 

56.5 
91.3 

50.7 
70.2 

65.7 
92.3 

50.0 
85.0 


h-i.2 

91.2 
50.5 

93.0 
89.0 

89.8 
81.5 

95.7 
98.0 

88.7 
81.8 
89.1 
95.5 

61.5 
65.0 
79.2 
72.5 

85.0 
129.0 
115.0 

82.5 
81.5 

87.5 

100.5 

92.0 

64.0 
95.4 
79.0 


in. 2 

"89.5 
105.6 

"78.2 
90.3 

84.7 
113.3 

'83.6 
104.6 




C, 0.44-0.50; 
Ni, 2.32-2.39. 

C, 0.32-0.34; 
Nl, 2.66-2.75. 

C, 0.30-0.35; 
Ni, 2.66-2.76. 

C, 0.16-0.21.... 

C, 0.63-0.72; 
Ni, 2.90-2.94. 

C, 0.31-0.35; 
Ni, 2.69-2.81. 

C, 0.22-0.25.... 


in.2 
48.8 

85.2 
252.0 

309.6 

34.5 
247.6 

16.3 
142.0 
432.0 

452.0 


in. 2 

187.0 
704.6 

48.4 
304.0 

16.1 
183.6 

456.6 


] Fairly fine withi 
1 coarse ferriteK, 
boundaries, lewL, 
J slaggy areas. J 

Fine uniform 

Very fine uniform 

1 Fir-tree crystals andl 
> a few slaggy fer-l Ingo- 
) rite areas. [tism 
Fine uniform. J 
Sorbitic, ferrite ghosts 

Finer than 3A. 1 Very 
Fairly uniform. 1 few 
Fine, uniform. [slaggy 
Do. J areas 

\Coarse with thick ferrite 
1 veins 

Fine, trace of veins 

Fine with streaks 

Coarse pearlite 
>Fine slaggy pearlite areas 

1 Fairly fine; ferrite veins, 

I slaggy areas 

I Ingotism 

Fine ; trace ferrite ghosts 
Very fine, pitted with holes 
Do. 

Fine, uniform 

Very fine, sorbitic, ferrite 

Very fine, all sorbitic 



X — inner zone. 
Y outer zone. 



T — tangential. 
N — normalized. 



Q — quenched and drawn. 

QQ — double -quenched and drawn. 



5. MACROSTRUCTURE AND MICROSTRUCTURE 

It is of interest to note there appeared no flaws or visible defects, 
other than small blowholes near the inner surface, in the prepara- 
tion of any of the test pieces for physical or chemical examination. 
The blowholes noted were always within about one-sixteenth inch 
from the inner or free surface of the casting. No hard spots 
were found in any of the castings. Just next the inner surface of 
all castings there is a layer not over one-sixteenth inch thick 
which appears to contain nearly all the physical and chemical 
discontinuities. 

vSulphur prints and cupric ammonium chloride etchings were 
made on transverse sections of each casting. Some of the sections 
photographed are shown on Figs. 3, 4, and 5, and represent the 
coarsest grained and most irregular portions of the sections 



12 



Technologic Papers of the Bureau of Standards 




B 




Fig. 3. — Transverse sections of castings Nos. I and 5 

(A) Casting No. 5: Nitric acid etching of a transverse section (X, about i}4). The structure is 
coarse grained with higher carbon areas in the inner zone 

(B) Casting No. 5: Sulphur print of a transverse section. There are small high-sulphur areas in 
the inner zone and several circumferential bands low in sulphur in the middle and outer 
zones 

(C) Casting No. 1: Cupric ammonium chloride etching of a transverse section. This structure 
is practically free from fir-tree crystals, but shows circumferential bands or zones apparently 
highest in carbon in the inner zone and lowest in carbon in the middle zone 



Tests of Centrifugally Cast Steel 



13 




B 



A 



Fig. 4. — Portion of transverse ring from casting No. 4 

(A) Sulphur print, actual size. There is little variation in the amount of sulphur, slightly 
more along inner edge than near outer edge. Several small local segregations may be seen 

(B) Cupric ammonium chloride etching (X 2). This shows the coarse-grained structure of 
the steel 



14 



Technologic Papers of the Bureau of Standards 



examined. The 7 2 -inch longitudinal section was finished and 
rubbed down with fine emery paper, and a sulphur print was taken 
along the entire length; no longitudinal segregation was found. 





A B 

Fig. 5. — Portion of transverse section of casting No. J 

(A) Sulphur print, actual size. This shows practically no segregation of sulphur 
except a few small spots at the extreme inner edge where small surface blow- 
holes occur 

(B) Cupric ammonium chloride etching, actual size. This is a portion of the 
transverse section (full thickness of cylinder as cast, no machining) and shows 
the steel to be free from ingotism. There are small surface blowholes, all 
within xV inch of the surface. The inner zone (zone 3) is slightly higher in 
carbon. 

At one point a hole or blister, 2 inches long, yi inch wide, was found 
■^2 inch from inside edge of the casting and a distance of 6 inches 
from one end. Fig. 3A, a nitric acid etching of the entire section, 



Tests of Centrifugally Cast Steel 15 

revealed nothing that is not shown in the sulphur prints. Any 
appreciable segregation in the casting occurs transversely from 
outside to inside, as shown in the etched transverse section. 

Specimens for microscopic examination were cut from transverse, 
radial (longitudinal), and tangential sections of each casting as 
received, and from transverse sections of the heat-treated bars; 
that is, after normalizing, quenching, and drawing, and double- 
quenching and drawing. Photomicrographs taken at a magnifica- 
tion of 50 diameters are shown and described in Figs. 4 to ga. 
Each casting was found to contain relatively large ferrite areas 
(locally decarburized areas) or long ferrite veins (outlining very 
coarse primary crystals). 

The most serious of the low-carbon areas were found in castings 
Nos. 3 A and 6 (Figs. 7 and 8). These areas are not completely 
eliminated by normalizing, and persist even after quenching and 
drawing, but have been almost completely eliminated by the 
double-quench and draw treatment. The normalizing treatment, 
for the most part, greatly refines the structures, while quenching 
and drawing produces a sorbitic structure with partially diffused 
ferrite. Structures after the double-quench and draw compare 
favorably with those of large heat-treated steel forgings. 

IV. SUMMARY 

There were examined a miscellaneous lot of five castings in the 
form of cylinders of wall thickness 8}4 inches to y 2 inch, made by 
the Millspaugh centrifugal process. Their composition ranged 
from two low-carbon steels, C=o.i7 and 0.23 per cent, to three 
nickel steels ranging in carbon from 0=0.33, 0.46, to 0.66 per 
cent, and in nickel from Ni = 2.69, 2.35, to 2.92 per cent. 

Segregation of the elements carbon, phosphorus, sulphur, nickel, 
and copper appears to exist to a slight extent, but only radially, 
and is most marked next the inner surface in a narrow zone of 
about one-sixteenth inch depth. Manganese and silicon do not 
segregate in this type of casting. The greatest carbon segregation 
was 0.09 per cent in nickel steel (C=o.66, Ni = 2.92 per cent) and 
the least was 0.02 per cent in another nickel steel (0=0.33, Ni = 
2.69 per cent). 

The hardness (Brinell and scleroscope) practically follows the 
segregation. 

The only evidence of unsoundness was the presence of small 
blowholes in the inner zone, usually within one-sixteenth inch 
of surface. 



i6 



Technologic Papers of the Bureau of Standards 




A 




B 

Fig. 6. — Casting No. 5. Etched with picric acid. X 50 

(A) Transverse section. This steel is very coarse grained and apparently has not been 
annealed. The average structure consists of pearlite with a thin, polyhedral network 
of ferrite and is fairly uniform except the zone (about Ji nch deep) adjacent to the bore, 
where there are large areas eutectoid in structure about jo points higher in carbon than 
the average structure 

(B) Radial, longitudinal section. This is similar to the transverse section 



Tests of Centrifugally Cast Steel 



17 




c 




D 

Fig. 6a. — Casting No. 5 as cast and normalized. Etched with picric acid. 

X 5° 

(C) Tangential section as cast. This structure is slightly finer than that of the transverse 
and radial sections (see Fig. 6) 

(D) Normalized. The grain has been greatly refined by this treatment, but traces of 
ferrite areas containing slag inclusions still remain. The ferrite network has not been 
entirely eliminated. A few small blowholes may be seen 



1 8 



Technologic Papers of the Bureau of Standards 




c 

Fig. 7. — Casting No. 6 as cast. Etched with picric acid. X 50 

(A) Transverse section. This casting, although not annealed, has a fine-grained structure. Traces 
of fir-tree crystals are found near the inner edges, and coarse primary crystals are outlined by a 
thin ferrite network, but no slaggy ferrite areas appear in this section 

(B) Radial section. This shows more pronounced fir-tree crystals than the transverse section 

(C) Tangential section. A cluster of slaggy low-carbon areas appears in this section. Traces of 
fir-tree crystals were found also 



Tests of Centrifugally Cast Steel 



19 




Fig. 8. — Casting No. 6 etched with pircic acid. X 50 

(A) Normalized. A fairly uniform, fine-grained ferrite-pearlite structure has been produced. No ferrite 
veins were found 

(B) Water quenched and drawn. This structure is sorbitic with a fine network of undiffused ferrite. 
Slight traces of ferrite veins, partially broken up, were found 

(C) Double-quenched and drawn. Although the structure has been greatly refined and the ferrite well 
diffused, shadowy traces of ferrite veins remain. An area pitted with tiny holes is here shown 



20 



Technologic Papers of the Bureau of Standards 




Fig. 9. — Casting No. 7 (basic open-hearth steel) etched with picric acid. X 50 

(A) Transverse section, as received. There is a fine-grained uniform ferrite-pearlite structure free from 
blowholes, segregation, or slag. The steel has been well annealed 

(B) Radial (longitudinal) section as received. This structure is similar to that of the transverse section 

(C) Tangential section, as received. The structure is fine grained but has a few areas containing needle- 
like ferrite particles, indicating incomplete annealing 



Tests of Centrijugally Cast Steel 



21 




D 




E 

Fig. ga. — Casting No. J. Transverse section etched with picric acid. X. 50 

(D) After single heat treatment. The steel has a very fine sorbitic structure with a ferrite 
network, and a few ferrite areas not fully broken up 

(E) After double heat treatment. The structure is fine and sorbitic. The network has 
been broken up, but many ferrite areas still remain 



22 Technologic Papers of the Bureau of Standards 

The density across a section is practically constant; that is, 
to 0.004 i n 7-836- 

The mechanical properties show, in general, somewhat greater 
strength, elastic limit, and resistance to shock, but less ductility, 
in the tangential than in the longitudinal direction. 

The internal stresses developed in the castings by this centrifugal 
process of manufacture, as determined from measurements on 
three rings from each of two castings, show values of the order of 
the elastic limit with the outer zones in compression. 

The effect of heat treatment in improving the physical properties 
of the castings is very marked. The results suggest that the 
properties of such castings suitably treated may rival those of 
forgings of the same chemical composition. 

The micro structure of at least some of these castings is better 
than that ot ordinary castings; certain ones show pronounced 
ingotisms (dendritic structure). The nickel steels contain more 
slag inclusions than is usual in ordnance steel, showing that this 
centrifugal process may not clear up a basic steel. The ingotism 
and coarse grained structures of these centrifugal castings can, in 
general, be removed only by prolonged and repeated heat treat- 
ments; that is, normalizing followed by double-quench and draw. 

The above account is limited to a description of the tests, and 
no references are given as to the details of the manufacturing 
operations, since we had no first-hand information concerning 
them. 

Acknowledgments should be made to the members of the staff 
of the divisions of chemistry, structural materials, and metallurgy 
who assisted in these tests and in particular to G. N. Nauss, who 
followed them through in detail. 

Washington, February 11, 1921. 



